IIc hard drives are scarcer than honest polititions, I'd forget about finding
one.
There's a FAQ on this at
ftp://apple.cabi.net/pub/applegs/FAQs.and.INFO/A2.Csa2.FAQs/Csa2HDNSCSI.txt
Take a look at it and if you have more question or if you find it confusing we
can go from there.
Wayne